Box plots of variation in MRM quantitative measurements, interlaboratory CV, and intralaboratory CV. All CV calculations are performed on the original data, while log-scaled axes are used to enchance visualization in the plots. (a) Intralaboratory assay CV. Box plots showing measured log concentration (y axis) versus theoretical (spiked-in) concentration (x axis) for HRP-SSD across the entire concentration range in diluted plasma. Protein concentration in mg/ml is mg protein equivalent in 1 ml undiluted plasma. The box plots for studies I and II are based on four replicate measurements, whereas those for study III summarize 12 measurements (four from each of 3 process replicates). Each of the eight sites was assigned a random numerical code (19, 52, 54, 56, 65, 73, 86, 95) for anonymization. (b) Interlaboratory assay CV. Values are shown for studies I-III for the entire range of HRP-SSD final analyte concentrations in plasma. Within each box plot, actual intralaboratory CV values for individual laboratories are shown with color-coded markers. The CV values are calculated based on the single best performing transition (lowest combined CV) across studies I and II. This same transition is also used for study III. Adapted from Addona, et. al., Nature Biotechnology, 27(7):633-41 .